javascript - HTML5 Canvas pie chart

Question

I'm attempting to create a simple pie chart like shown in the graphic below:

The chart will show the results for a quiz where a user can choose either a, b or c. They're 10 questions and the user can only choose one option per question.

What I want to do is show the pie chart with each segment being a percentage of 100% by passing in the values for either a,b, or c.

I have the following so far:

var greenOne = "#95B524";
var greenTwo = "#AFCC4C";
var greenThree = "#C1DD54";

function CreatePieChart() {
  var chart = document.getElementById('piechart');
  var canvas = chart.getContext('2d');
  canvas.clearRect(0, 0, chart.width, chart.height);

  var total = 100;

  var a = 3;
  var b = 4;
  var c = 3;

  for (var i = 0; i < 3; i++) {
    canvas.fillStyle = "#95B524";
    canvas.beginPath();
    canvas.strokeStyle = "#fff";
    canvas.lineWidth = 3;
    canvas.arc(100, 100, 100, 0, Math.PI * 2, true);
    canvas.closePath();
    canvas.stroke();
    canvas.fill();
  }
}
CreatePieChart();

<canvas id="piechart" width="200" height="200"></canvas>

Answer 1

Even after searching Google and triple-checking my radians values, etc. I was still having trouble with this, so I have created a jsFiddle for people to play with as a live example and will post the code below as well. (Update: in the fiddle v2, stroke and labels are added also.)

var canvas = document.getElementById("can");
var ctx = canvas.getContext("2d");
var lastend = 0;
var data = [200, 60, 15]; // If you add more data values make sure you add more colors
var myTotal = 0; // Automatically calculated so don't touch
var myColor = ['red', 'green', 'blue']; // Colors of each slice

for (var e = 0; e < data.length; e++) {
  myTotal += data[e];
}

for (var i = 0; i < data.length; i++) {
  ctx.fillStyle = myColor[i];
  ctx.beginPath();
  ctx.moveTo(canvas.width / 2, canvas.height / 2);
  // Arc Parameters: x, y, radius, startingAngle (radians), endingAngle (radians), antiClockwise (boolean)
  ctx.arc(canvas.width / 2, canvas.height / 2, canvas.height / 2, lastend, lastend + (Math.PI * 2 * (data[i] / myTotal)), false);
  ctx.lineTo(canvas.width / 2, canvas.height / 2);
  ctx.fill();
  lastend += Math.PI * 2 * (data[i] / myTotal);
}

<canvas id="can" width="200" height="200" />